Absolute zero is the lowest temperature that can be obtained for a material. Temperature is actually a measure of how hot or cold an object is and describes how fast the atoms or molecules are moving or vibrating.
There are three scales that are commonly used to measure temperature: Fahrenheit, Celsius, and Kelvin. These are all relative measurements of the temperature to absolute zero. On the Fahrenheit scale, water freezes at 32 oF. On the Celsius scale, the freezing point of water occurs at 0 oC and in Kelvin this occurs at 273K.
Absolute Zero is defined as 0 K on the Kelvin temperature scale. This would correspond to –273 oC and –459 oF. Scientists prefer to use the Kelvin temperature scale, particularly if they work at very low temperatures.
At high temperatures such as when water boils, the atoms and molecules in matter move very fast and have a great deal of energy. As the substance cools, energy is removed from the substance and the motion of the atoms and molecules decreases and they begin to move slower. This continues as the material approaches absolute zero with the atomic motion decreasing and the atoms and molecules getting closer together.
According to kinetic theory, at absolute zero all atomic and molecular motion stops. If that were the case, any material at absolute zero would be a solid. However, this has been shown to be false. In fact, scientists have shown that at absolute zero matter is better described as having reached a lowest energy state where no more energy can be removed. But, the vibrations of the molecules never come to a complete stop.
In the laboratory, scientists commonly work at temperatures as low as 4 K using liquid helium and temperatures as low as 250 pK (2.50 x 10-10 K) have been achieved. The coldest place found in nature is the Boomerang nebula, which is 5,000 light-years from Earth in the constellation Centaurus and has been measured at 1 K.